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HomeMy WebLinkAboutSite Certifications - 01/26/2007January 26, 2007 Project No. 1646-01-98 (ESL A R Jay Barber City of Ft. Collins Stormwater Utility P.O. Box 580 Ft. Collins, Colorado 80524 Re: Old Town North; Fort Collins, Colorado Drainage Certification Dear Jay, This letter serves as final drainage certification for Old Town North. Shear Engineering Corporation has been involved. throughout construction and has coordinated as -built requirements. Shear Engineering Corporation has made several walkthroughs with representatives of Hall -Irwin Construction and Palladian Construction. and has directed field modifications that were required to meet compliance with the design intent of the approved Final Utility Plans for Old Town North prepared by Shear Engineering Corporation; Shear Project No: 1646-01-98; City Engineer approval date 03/02/04. As -built survey shots for the Detention Pond were provided by Ayres Associates Inc. of Fort Collins and the resultant contours were analyzed by Shear Engineering Corporation.. Contour areas and stage -storage volume relationships were prepared and compared to those prepared during the final design of Old Town North. Volumes provided comply with the requirements of the approved Final Drainage and Erosion Control Report for Old Town North Phase 1 by Shear Engineering Corporation; S.E.C. Project No. 1646-01-98; Report dated March, 2002 except as discussed in further detail below. The following is a summary of the detention pond design parameters and construction results. Old Town North Detention Pond summary Design Outfall structure invert elevation 4957.97 100-year Water surface elevation 496025 100-year emergency overflow elevatio 4960.55 0 of detention and berm elevation 4961.50 Volume (cubic feet) 359370 Volume (acre feet) 8.25 Construction 4957.97 4960.09 4960.13 4961.50 359370 A 0.00 -0.16 -0.42 0.00 0.00 0.00 4836 S. College, Suite 12 Ft. Collins, CO 80525 (970) 226-5334 Fax (970) 282-0311 www.shearengineering.com PAGE 2 January 26, 2007 Project No. 1646-01-98 Re: Old Town North; Fort Collins, Colorado Drainage Certification The difference in elevation between design and construction for the 100-year emergency overflow elevation is 5". Refer to discussion below for additional detail. Attached is the As -Built Detention Pond Volume Rating Curve based on the as -built shots provided by Ayres Associates Inc. of Fort Collins. Also attached is an as -built of the detention pond showing spot elevations and resultant contours. This plan is provided at a scale that allows for overlaying on the original approved plan. The design grading plan for the detention pond is also provided. Additional detailed discussion is required for certain detailed drainage related issues. Detention Pond Emergency Overflow Weir The Colorado Department of Transportation owns the property south of the detention pond, a part of which is situated north of the Lake Canal. The proposed ten foot (10') concrete bike path was planned for this area. Due to the lack of cooperation from the Colorado Department of Transportation in allowing an easement or a license to install the ten foot (10') concrete bike path partially on CDOT property, the ten foot (10') concrete bike path will be installed at the top of the 10' wide detention pond berm and emergency overflow. The specified thickness of concrete for the ten foot (10') concrete bike path is 5". The bike path cost has been escrowed. The bike path will be installed at a future date. To meet ultimate detention pond design requirements, the emergency overflow elevation was adjusted to five inches (5") below the emergency overflow elevation of 4960.55 (elevation = 4960.13). The design 100-year water surface elevation is 4960.25. The actual 100-year water surface elevation is 4960.09. This is slightly below the temporary 100-year emergency overflow elevation (4960.13). Lake Canal Emergency Overflow Weir An emergency overflow spillway was specified to be cut into the existing irrigation structure located at the confluence of the Dry Creek channel flowline and the Lake Canal. The emergency overflow spillway has not been provided as of the date of this certification. A letter provided by the Lake Canal Company indicated a concern with the structural integrity of the structure. A copy of the letter is attached for immediate reference. Also attached is a detail graphic of the exiting structure noting limits of stone and concrete. The weir was specified to be cut at a 1.90' depth from the top. This was based on actual ditch flow requirements and existing grades along the ditch adjacent to the project site. Providing the overflow weir may require structural stabilization of the structure due to the combination concrete and stone. PAGE 3 January 26, 2007 Project No. 1646-01-98 Re: Old Town North; Fort Collins, Colorado Drainage Certification The following concerns expressed by City staff during construction were also addressed: ❑ Ponding at the northeast corner of the intersection of Redwood Street and Vine Drive ❑ Verification of rip rap placement for the Detention Pond emergency overflow was documented ❑ Detention pond sump area pump installation has been completed. Except for the emergency overflow spillway specified to be cut into the existing irrigation structure located at the confluence of the Dry Creek channel flowline and the Lake Canal, all drainage facilities for Old Town North have been installed in general conformance with the approved Final Utility Plans for Old Town North and are functioning appropriately and generally meet the intent of the original drainage design for Old Town North in accordance with the approved Final Drainage and Erosion Control Report for Old Town North Phase 1 by Shear Engineering Corporation; S.E.C. Project No. 1646-01-98; Report dated March, 2002. ;e certification, please call at (970) 226-5334. Shear Engineering BWS / me attachments • A copy of the letter from Lake Canal • As -Built Detention Pond Volume Rating Curve • Detail of the Lake Canal irrigation structure • as -built topo and spot elevations for the Detention Pond • Original grading plan for the detention pond cc: Monica Sweere; Palladian Construction Co. Ken Lambrecht; Hall -Irwin Construction THE LAKE CANAL COMPANY THE LAKE CANAL RESERVOIR COMPANY November 1, 2005 Brian Shear Shear Engineering 4836 South College Avenue Fort Collins, Co 80525 RE: Old Town.North Brian: En (970) 352-0222 During the construction of infrastructure for Old Town North, there were plans to remove a portion of an old rock structure in the Dry Creek channel for storm water purposes. I looked at that structure with Chris Sweet during construction. Due the fact that irrigation season was nearing, there is concern that partial demolition of the structure will cause problems with structural integrity and there are no plans for reinforcing the existing structure or replacing the existing structure. I am writing you because it is my understanding that this issue is impacting Hall Irwin. It is my opinion that the issue lies between two or more of The Lake Canal Company, Shear Engineering, Old Town North and the City of Fort Collins. Hail Irwin, in my opinion, has responded properly in not moving forward on this specific issue so as not to exasperate an existing problem. Plans should be started to address this issue before water from this site or area is inadvertently passed down the canal to other properties. Please give me a call if you have questions. Sincerely, Don Magnuson Superintendent 33040 Railroad Avenue • P.O. Box 104 • Lucerne, Colorado 80646 Old Town North Detention Pond As -Built Detention Pond Volume Rating Curve 4955.72 0 1.49 0.000 0.000 4956.00 4,218 1.490 0.009 0.009 4957.00 54,949 1.000 0.569 0.578 4958.00 89,520 1.080 1.641 2.218 4959.00 120,475 1.160 2.399 4.618 4960.00 167,980 1.250 3.293 7.910 4960.25 176,888 1.330 0.989 8.899 (100 year Volume+ WQCV) Required = 8.25 acre-ft WQCV Required = 0.850 acre-ft Voulme at Temporary Weir Elev. _ acre-ft As -Built Report 100-year WSEL = 4960.25 WQ WSEL = 4957.37 Temp. Weir Elev. _ n/a V = 3d(A+B+ AB) where: V = volume between contour interval d = elevation,, - elevation,_, A = area of elevationn_1 contour B = area of elevations contour 8:37 AM Ernst Engineering, LLC 1/26/2007 9 �utai t!7 � Rept�� Date 1 SHEAR FINAL DRAINAGE AND EROSION CONTROL REPORT For OLD TOWN NORTH PHASE 1 Ft. Collins, Colorado Prepared for: OLD TOWN NORTH LLC PO Box 270053 Ft. Collins, CO 80527-0053 Prepared By: SHEAR ENGINEERING CORPORATION Project No: 1646-01-98 Date: March, 2002 4836 S. College, Suite 12 Ft. Collins, CO 80525 (970) 22G5334 Fax (970) 282-0311 wwwshearengineering.com i Project No.: 1646-01-98 Re: Final Drainage and Erosion Control Report Old Town North — Phase I Match, 2002 3. A portion of the storm sewer outfall from the detention pond will be constructed on the east side of Redwood Drive. This portion of the storm sewer will be constructed in Tract A of Redwood Village P.U.D. Phase II. Redwood Village P.U.D. Phase II is platted. Tract A was dedicated as an Access, Drainage, Utility and Maintenance Easement with the final plat of Redwood Village P.U.D. Phase H. a. A Type 2 outlet structure is specified within the limits of the berm. The top of the 5' x 5' outlet structure is set above the required 100-year WSEL for the 100-year storm. An 18" high by 32" wide rectangular orifice will be placed within the outlet structure to restrict flows to required 13.20 cfs. The outlet structure will function as a 20-foot broadcrested weir. The top of the box is set so that the required WSEL is reached in the pond. The top of the box is set at an elevation of 4960.47 feet. Refer to the Storm Sewer, Drainage and Erosion Control Detail Sheet located within the plan set for reference. Additional specifications regarding the outlet box are located in Appendix I attached to this report. 4. A 24" RCP pipe will convey the released stormwater to the existing irrigation structure as agreed to by the Lake Canal Company. The pipe has a capacity of 20.79 cfs based on Manning's equation. Since the pipe will be flowing under pressure, R4 joints are specified on the plan and profile. An emergency overflow weir is specified within the limits of the berm to pass flows directly into the Lake Canal in case the orifice and outlet structure are completely plugged. The emergency overflow weir is sized to pass the 100-year peak flow (Q 100) to the pond. a. The Q100 to the pond is 160.46 cfs. b. The weir is set at an elevation of 4960.55 feet. c. The weir length is 70.00 feet. d. The weir is sized to allow the Q100 to pass with a maximum head of 0.95 feet. e. The maximum WSEL if the weir were to be functioning alone is 4961.47 feet. F. The maximum WSEL if the weir were functioning in tandem with the orifice and the primary weir is 4961.23 feet. g. Buried class M riprap (D50 = 12") is specified at the weir and down the bank to the Lake Canal. E. SPECIFIC DETAILS - WQCV 1. Water Quality control measures are specified on both the Drainage Plan sheet and Erosion Control Plan sheet. 2. Maintenance of water quality control devices will remain the responsibility of the contractor and the owner until the project is complete. Page 13 Project No.: 1646-01-98 Re: Final Drainage and Erosion Control Report Old Town North — Phase 1 March. 2002 7. A storm sewer is proposed for Interim Redwood Street further south of storm sewer "I"'. An 18" RCP is proposed to cross Interim Redwood Street just north of the intersection of Interim Redwood Street and East Vine Drive. This storm sewer is only temporary and will be removed once the Ultimate Redwood Street construction is completed. The storm sewer is shown graphically as storm sewer profile "H". 8. A storm sewer is proposed for Ultimate Redwood Street. An 18" RCP is proposed to cross the Ultimate Redwood Street between two 10' Type R inlets just north of the intersection of Ultimate Redwood Street and East Vine Drive. This will be the final design and is shown as storm sewer profile "G". 9. A 24" storm sewer is proposed for conveying storm water from the pond to an existing concrete weir located within the Lake Canal. The storm sewer runs along the south side of the pond and continues northeast until it intersects with the Lake Canal. The storm sewer is shown graphically as storm sewer profile "I". 10. An 18" storm sewer is proposed in realigned Vine Drive to convey stormwater from a low point located west of Jerome Street to the proposed Dry Creek Channel. The final design and construction of this storm sewer will be completed in future phases. The storm sewer is shown graphically as storm sewer profile "J". 11. SPECIFIC DETAILS —LAKE CANAL /LAKE CANAL OVERFLOW 1. The existing irrigation structure blocks the Dry Creek drainageway. An emergency overflow spillway will be constructed in the east wall of the existing irrigation structure. The overflow structure is sized to pass the developed peak flows from the site for the 100-year event (Q 100). a. Approximately 150 cfs is conveyed in the Lake Canal for irrigation purposes. i. The calculated flow depth for the irrigation flows across the structure is 1.91 feet. ii. The capacity of the irrigation structure is 617.71 cfs while flowing full. This data is found in the Lake Canal Overflow section of Appendix I. b. The Lake Canal conveys 150 cfs for irrigation purposes. i. The calculated flow depth of the Lake Canal with 150 cfs flowing is approximately 2.67 feet. ii. The capacity of the Lake Canal is 297.95 cfs, this value is found assuming the canal is flowing full at a depth of four feet. This data is found in the Lake Canal Overflow section of Appendix I. iii. A combination of the maximum ditch flow requirement of 150 cfs, and the 100-year overflow from the pond in emergency situations (160.46 cfs), results in a potential total flow in the ditch of 310.46 cfs. This is approximately 12.50 cfs more than the calculated theoretical capacity of the Lake Canal. Overflow in emergency situations is minimal, Page 19 Project No.: 1646-01-98 Re: Final Drainage and Erosion Control Report Old Town North — Phase 1 March, 2002 iv. One concern with the additional 12.50 cfs is that it could possibly flood structures located south of the Lake Canal. The Lake Canal could essentially act as a 1500 foot broadcrested weir from Jerome Street to Redwood Street. With this assumption a weir calculation can be performed to determine the head that would be overflowing the ditch. With a discharge of 12.50 cfs and assuming a 1500 foot broadcrested weir, the head that would overflow the ditch would be approximately 0.055 feet. This is an insignificant amount of water to flood any structure in the area. The flows would spread out over an area of about 2.5 acres before it would reach any structures, therefore, eliminating any danger of flooding. A calculation verifying the discussed information is found in the Lake Canal section of Appendix I. c. A 4' high x 20' wide box culvert will be placed within the Lake Canal at the proposed Redwood Street crossing. i. The calculated flow depth for the box culvert assuming 150 cfs is flowing through the culvert is approximately 1.55 feet. ii. The capacity of the box culvert is 637.80 cfs assuming the culvert is flowing full at four feet high. This data is found in the Lake Canal Overflow section of Appendix I. d. The Q100 to the detention pond is 160.46 cfs. e. The 25' weir will be set 3.0 feet above the floor of the structure to ensure that the irrigation flows stay in the canal. A 25' notch will be cut into the east wall of the structure and the grading east of the structure will be modified to allow the excess flows to spill over the weir and into the historic Dry Creek channel. VI. EROSION CONTROL: A. GENERAL CONCEPT i. Erosion control measures are specified on the Erosion Control Plan. 2. Maintenance of erosion control devices will remain the responsibility of the contractor and the owner until the project is complete. B. SPECIFIC DETAILS 1. The following temporary measures are specified on the Erosion Control Plan: a. A silt fence shall be installed around the entire Phase 1 portion of the project. The location of the silt fence shall be at the base of all grading improvements, roughly along property lines. The only exception to this is at the improvements along the north side of existing Vine Street. No silt fencing will be incorporated with the existing Vine Street improvements. b. A gravel inlet filter shall be included in front of the orifice plate at the water quality inlet box, located at the sump of the detention pond. The gravel inlet Page 20 THE LAKE CANAL COMPANY THE LAKE CANAL RESERVOIR COMPANY (970) 352-0222 November 1, 2005 Brian Shear Shear Engineering 4836 South College Avenue Fort Collins, Co 80525 RE: Old Town North :o., During the construction of infrastructure for Old Town North, there were plans to remove a portion of an old rock structure in the Dry Creek channel for storm water purposes. I looked at that structure with Chris Sweet during construction. Due the fact that irrigation season was nearing, there is concern that partial demolition of the structure will cause problems with structural integrity and there are no plans for reinforcing the existing structure or replacing the existing structure. I am writing you because it is my understanding that this issue is impacting Hall Irwin. It is my opinion that the issue lies between two or more of The Lake Canal Company, Shear Engineering, Old Town North and the City of Fort Collins. Hall Irwin, in my opinion, has responded properly in not moving forward on this specific issue so as not to exasperate an existing problem. Plans should be started to address this issue before water from this site or area is inadvertently passed down the canal to other properties. Please give me a call if you have questions. Sinc erely, Superintendent 33040 Railroad Avenue • P.O. Box 104 • Lucerne, Colorado 80646 r S7o / Tvt*-v Av a 3 6 TYP��4/ �eacre�� � Sf�Ne S7 T� z_o 4. 0 No Text 4- or i. MAW"- �7 v.wA io 414 It flL CR 14 --aA I No Text i t r' j - - �, a --- fay I c a - - Y,e — - - 1 I- - 4-+h AJET,gN fig' a �M ) r �♦ f � -♦s a NOTES: 1. FOR MAXIMUM ALL0WA0l£ RNISHED i6 GRACES 6G) SEE MEET 90 (DRAIN E ADD ERO9g1 C mm MOMS), j rFE 3 MMIecIOF \ MI wam 4N4 IN 1 S M \ 1 � r j r Lisa �, rn-m BLOCK I � me _ R( Arl-N. 96000.37� I! 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